Apparatus and systems used for air conditioning (AC) refrigerant recovery typically are required to meet a certain level of recovery efficiency. The need to provide for recovery efficiency is important to reduce emissions of refrigerant during the recovery process and to provide for accurate recharging, such as for mobile AC systems.
A SAE Surface Vehicle Standard has been issued, SAE J2788, in December of 2006. This SAE standard implements a refrigerant recovery standard for mobile AC systems to achieve a 95% refrigerant recovery efficiency in 30 minutes or less, based upon a 3 lb capacity General Motors (GM) specified system. See, Section 7.1.1 of the SAE J2788 standard.
U.S. Pat. No. 5,325,675, entitled “Refrigerant Handling System and Method With Enhanced Recovery Vacuum Capacity” provides a method wherein the refrigerant compressor can be employed alone for drawing refrigerant down to a pressure of one atmosphere (zero psig, 29.9 inches of mercury), and then the vacuum pump is then operatively connected in series with the compressor to assist the compressor in drawing a deeper inlet vacuum, such as in the range of zero to twenty inches of mercury.
Typically, the aforementioned level of refrigerant recovery efficiency has been achieved by recovering the initial refrigerant from the system to zero psig using only the compressor of the refrigerant recovery apparatus (as in conventional recovery) and then pulling for a fixed period of time of 15 minutes, for example, with a vacuum pump of the refrigerant recovery apparatus in series with the compressor.
However, refrigerant recovery systems and methods that pull to a preset vacuum level, such as pulling to 0 psig with the compressor, and then running the vacuum pump in series with the compressor for the fixed period of time, do not take into consideration variations in ambient and vehicle temperature, as well as mobile AC system configuration differences, which can effect the time required to meet efficiency levels for refrigerant recovery.
For example, where pulling to zero psig with the SAE requirement for refrigerant recovery for the fixed period of time meets the SAE requirement for refrigerant recovery efficiency on a large mobile AC system, smaller mobile AC systems and different ambient conditions can require less time than the fixed period of time to meet the SAE requirement for refrigerant recovery efficiency.
Therefore, for mobile AC systems that require less than the fixed period of time to meet the refrigerant recovery efficiency, a service time penalty can result leading to increased operating costs and reduced efficiency as to the mobile AC systems that can be serviced over a period of time.
Accordingly, it is desirable in the AC recovery area for refrigerant recovery, as well as in other gas or liquid recovery, to provide recovery apparatus, systems and methods that utilize a variable period of time, rather than the fixed period of time, for gas or liquid recovery, for drawing down or evacuating a vessel or system, such as time period to run the vacuum pump with the compressor to meet the SAE requirement for refrigerant recovery efficiency for mobile AC systems, to promote reducing operating costs and increasing efficiency as to number of units that can be serviced over a period of time.